Mutant forms of herpesvirus saimiri (HVS) subgroup C strain 488 with deletions in either STP-C488 or Tip were constructed The transforming potentials of the HVS mutants were tested in cell culture and in common marmosets Parental "VS subgroup C strain 488 immortalized common marmoset T lymphocytes in vitro to interleukin-2-independent growth, but neither of the deletion mutants produced such growth transformation Wild-type "VS produced fatal lymphoma within 19 to 20 days of experimental infection of common marmosets, while "VS ASTP-C488 and "VS ATip were nononcogenic Virus was repeatedly isolated from the peripheral blood of marmosets infected with mutant virus for more than 5 months These results demonstrate that STP-C488 and Tip are not required for replication or persistence, but each is essential for transformation in cell culture and for lymphoma induction in common marmosets PUBLICATIONS Duboise, SM, Guo, J, Czajak, S, Desrosiers, RC and Jung, JU STP and Tip are Essential for Herpesvirus Saimiri Oncogenicity J Virol 1998; 72:1308-1313